From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 557FFC43331 for ; Thu, 5 Sep 2019 17:35:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 451A020828 for ; Thu, 5 Sep 2019 17:35:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391023AbfIERfS (ORCPT ); Thu, 5 Sep 2019 13:35:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:57716 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727143AbfIERfR (ORCPT ); Thu, 5 Sep 2019 13:35:17 -0400 Received: from oasis.local.home (bl11-233-114.dsl.telepac.pt [85.244.233.114]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9B2B3206A5; Thu, 5 Sep 2019 17:35:13 +0000 (UTC) Date: Thu, 5 Sep 2019 13:35:07 -0400 From: Steven Rostedt To: Suren Baghdasaryan Cc: Michal Hocko , Joel Fernandes , LKML , Tim Murray , Carmen Jackson , Mayank Gupta , Daniel Colascione , Minchan Kim , Andrew Morton , kernel-team , "Aneesh Kumar K.V" , Dan Williams , Jerome Glisse , linux-mm , Matthew Wilcox , Ralph Campbell , Vlastimil Babka , Tom Zanussi Subject: Re: [PATCH v2] mm: emit tracepoint when RSS changes by threshold Message-ID: <20190905133507.783c6c61@oasis.local.home> In-Reply-To: References: <20190903200905.198642-1-joel@joelfernandes.org> <20190904084508.GL3838@dhcp22.suse.cz> <20190904153258.GH240514@google.com> <20190904153759.GC3838@dhcp22.suse.cz> <20190904162808.GO240514@google.com> <20190905144310.GA14491@dhcp22.suse.cz> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ Added Tom ] On Thu, 5 Sep 2019 09:03:01 -0700 Suren Baghdasaryan wrote: > On Thu, Sep 5, 2019 at 7:43 AM Michal Hocko wrote: > > > > [Add Steven] > > > > On Wed 04-09-19 12:28:08, Joel Fernandes wrote: > > > On Wed, Sep 4, 2019 at 11:38 AM Michal Hocko wrote: > > > > > > > > On Wed 04-09-19 11:32:58, Joel Fernandes wrote: > > [...] > > > > > but also for reducing > > > > > tracing noise. Flooding the traces makes it less useful for long traces and > > > > > post-processing of traces. IOW, the overhead reduction is a bonus. > > > > > > > > This is not really anything special for this tracepoint though. > > > > Basically any tracepoint in a hot path is in the same situation and I do > > > > not see a point why each of them should really invent its own way to > > > > throttle. Maybe there is some way to do that in the tracing subsystem > > > > directly. > > > > > > I am not sure if there is a way to do this easily. Add to that, the fact that > > > you still have to call into trace events. Why call into it at all, if you can > > > filter in advance and have a sane filtering default? > > > > > > The bigger improvement with the threshold is the number of trace records are > > > almost halved by using a threshold. The number of records went from 4.6K to > > > 2.6K. > > > > Steven, would it be feasible to add a generic tracepoint throttling? > > I might misunderstand this but is the issue here actually throttling > of the sheer number of trace records or tracing large enough changes > to RSS that user might care about? Small changes happen all the time > but we are likely not interested in those. Surely we could postprocess > the traces to extract changes large enough to be interesting but why > capture uninteresting information in the first place? IOW the > throttling here should be based not on the time between traces but on > the amount of change of the traced signal. Maybe a generic facility > like that would be a good idea? You mean like add a trigger (or filter) that only traces if a field has changed since the last time the trace was hit? Hmm, I think we could possibly do that. Perhaps even now with histogram triggers? -- Steve